Inelastic processes in atomic, molecular and chemical physics (in honour of Andrey K. Belyaev)

Barklem, P. S.; Tscherbul, Timur V.

doi:10.1016/j.chemphys.2015.10.001

Cited by 8 publications

(10 citation statements)

References 39 publications

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“…Hydrogen collisions. For collisional excitation of Na and K we adopted data from Barklem et al (2012) and Barklem (2016Barklem ( , 2017a respectively. Those works cover the transitions between all levels from the ground state up to 5p for Na and 4f for K .…”

Section: Collisional Datamentioning

confidence: 99%

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NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

Osorio

Prieto

Hubený

et al. 2020

A&A

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Context. Relaxing the assumption of Local Thermodynamic Equilibrium (LTE) in modelling stellar spectra is a necessary step to determine chemical abundances better than about 10 % in late-type stars. Aims. In this paper we describe our efforts gearing up to perform multi-element (Na, Mg, K, and Ca) Non-LTE (NLTE) calculations that can be applied to the APOGEE survey. Methods. The new version of TLUSTY allows for the calculation of restricted NLTE in cool stars using pre-calculated opacity tables. We demonstrate that TLUSTY gives consistent results with MULTI, a well-tested code for NLTE in cool stars. We use TLUSTY to perform LTE and a series of NLTE calculations using all combinations of 1, 2, 3 and the 4 elements mentioned above simultaneously in NLTE. Results. In this work we take into account how departures from LTE in one element can affect others through changes in the opacities of Na, Mg, K, and Ca. We find that atomic Mg, which provides strong UV opacity, and exhibits significant departures from LTE in the low-energy states, can impact the NLTE populations of Ca, leading to abundance corrections as large as 0.07 dex. The differences in the derived abundances between the single-element and the multi-element cases can exceed those between the single-element NLTE determinations and an LTE analysis, warning that this is not always a second-order effect. By means of detailed tests for three stars with reliable atmospheric parameters (Arcturus, Procyon and the Sun) we conclude that our NLTE calculations provide abundance corrections that can amount in the optical up to 0.1, 0.2 and 0.7 dex for Ca, Na and K, but LTE is a good approximation for Mg. In the H-band, NLTE corrections are much smaller, and always under to 0.1 dex. The derived NLTE abundances in the optical and in the IR are consistent. For all four elements, in all three stars, NLTE line profiles fit better the observations than the LTE counterparts. Conclusions. The atomic elements in ionisation stages where over-ionisation is an important NLTE mechanism are likely affected by departures from LTE in Mg . Special care must be taken with the collisions adopted for high-lying levels when calculating NLTE profiles of lines in the H-band. The derived NLTE corrections in the optical and in the H-band differ, but the derived NLTE abundances are consistent between the two spectral regions.

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Section: Collisional Datamentioning

confidence: 99%

“…Charge transfer processes like A + H ↔ A + + H − were calculated by Barklem et al (2012) and Barklem (2016Barklem ( , 2017a for Na and K respectively and are included in this work. Figure 2 shows the rate coefficients obtained at 5 000 K for the different collisional processes described above for the Na and K atoms.…”

Section: Collisional Datamentioning

confidence: 99%

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

Osorio

Prieto

Hubený

et al. 2020

A&A

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“…For instance, we can mention the neutralization cross-sections, which depend critically of the positions of the avoided crossing series and their great importance for charge transfers in diverse astrophysical environments. [66][67][68][69] From…”

Section: Electronic Energy Curvesmentioning

confidence: 99%

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH⁺)

Habli

Mejrissi

Issaoui

et al. 2014

Int J of Quantum Chemistry

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The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 molecular states dissociating up to Sr2+ + H− using an ab initio approach. The ab initio formalism is based on large basis sets, nonempirical atomic pseudopotential for strontium core, correlation treatment for core valence through the effective core polarization potentials and for valence through full valence configuration interaction. Our theoretical molecular constants match published values very well and a large amount of new results is produced. Unusual potential shapes are found in 1Σ+ states often caused by avoided crossing series between them and imprinted by the ionic state Sr2+H−. The high potential energy curves suggest, it is possible to form H− or at least to neutralize H+ in collisions with strontium. © 2014 Wiley Periodicals, Inc.

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“…A typical issue in non-LTE models arises from uncertainties in reactive or inelastic collisional rate coefficients (or cross sections) involving hydrogen atoms. Among these processes, mutual neutralization (MN) in ion-pair collisions plays an important role in thermalizing atoms owing to the large corresponding cross sections Barklem et al 2003). In MN reactions, oppositelycharged ions collide, resulting in the formation of neutral fragments following electron transfer from the anion to the cation.…”

Section: Introductionmentioning

confidence: 99%

Mutual Neutralization in Li⁺−D⁻ Collisions: A Combined Experimental and Theoretical Study

Launoy

Loreau

Dochain³

et al. 2019

ApJ

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We present a combined experimental and theoretical study of the mutual neutralization process in collisions of lithium ions (Li + ) with deuterium anions (D − ) at collision energies below 1 eV. We employ a merged-beam apparatus to determine total and state-to-state mutual neutralization cross sections. We perform nuclear dynamics calculations using the multi-channel Landau-Zener model based on accurate ab initio molecular data. We obtain an excellent agreement between the experimental and theoretical results over the energy range covered in this work. We show that the basis sets used in the ab initio calculations have a limited influence on the total cross section, but strongly impacts the results obtained for the partial cross sections or the reaction branching ratios. This demonstrates the important role of high-precision measurements to validate the theoretical approaches used to study gas-phase reactive processes. Finally, we compute mutual neutralization rate coefficients for Li + + H − and Li + + D − , and discuss their significance for astrochemistry models.

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Inelastic processes in atomic, molecular and chemical physics (in honour of Andrey K. Belyaev)

Cited by 8 publications

References 39 publications

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH⁺)

Mutual Neutralization in Li⁺−D⁻ Collisions: A Combined Experimental and Theoretical Study

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Inelastic processes in atomic, molecular and chemical physics (in honour of Andrey K. Belyaev)

Cited by 8 publications

References 39 publications

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

NLTE for APOGEE: simultaneous multi-element NLTE radiative transfer

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH+)

Mutual Neutralization in Li+−D− Collisions: A Combined Experimental and Theoretical Study

Contact Info

Product

Resources

About

Ab initio calculation of the electronic structure of the strontium hydride ion (SrH⁺)

Mutual Neutralization in Li⁺−D⁻ Collisions: A Combined Experimental and Theoretical Study